Electrical – How to design the A-B amplifier? I mean I have understood the working but how do i choose the values

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We have a college project to make an A-B amplifier. I have a basic layout of the transistor amplifier. Plus i have chosen the transistors I want. There are : 2N4401 (NPN) and 2N4403 (PNP).

1)My source is a song being played from my mobile. Here I have taken an AC Voltage of 16pk.
2) How do I modify my circuit for it.I realised Higher the Vcc value I take, the output increases more. Why? And what would be the ideal value?
3)Have I selected the wrong diodes? If I have so which one is suitable for the transistors I have chosen?
4)Why is my positive output waveform increasing with each increasing second?Also why is my Ie of npn decreasing?

Finally

EDIT 1: I Have changed the circuit after comparing it more carefully with the suggestions other users have given me. The Schematic is attached below with the output. I noticed other users complaining that my questions have been made blindly. Hence, I have been more precise now.
My Input here is a song being played from my mobile/smartphone. I will connect to the amplifier using it's audio jack. Thus, the song will be played on the speaker (here RL).
Firstly, when I make it on a breadboard the input here will be the song right? So, will the song even play (w/t distortion). Cause, Here I have taken a sine wave input and according to the simulation it is just increasing the amplitude.
Secondly, As pointed out by @jock my knowledge of the amplifier design is limited. I have seen probably all the videos relating to this amplifier on youtube . So, I know it's working but I am really confused about how to design one. Is there anywhere I can read up on this?
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Best Answer

You've said the following that I can understand, regarding the design:

  • Accept mobile output. (Which I can only assume means "headphone" jack.)
  • Use 2N4401 and 2N4403 for output BJTs. (That's specific enough.)
  • Class AB amplifier (using a complementary emitter follower topology, taken as a specification gathered from your schematic.)

You've said the following that I cannot understand, regarding the design:

  • "mobile" and "AC Voltage of 16pk" -- "Mobile" usually means "headphone" output, to me. But headphones are typically \$32\:\Omega\$, mostly resistive, and generally you don't see more than perhaps \$1.5\:\textrm{V}_{RMS}\$ there. Certainly, I can't recall ever seeing anything like \$16\:\textrm{V}_{PEAK}\$. Your AC simulation voltage source is set up that way. But I can't for the life of me guess why. Are you expecting some prior stage to provide that kind of signal? Where did this come from, exactly?
  1. My source is a song being played from my mobile. Here I have taken an AC Voltage of 16pk.

I don't understand much of this. See above.

  1. How do I modify my circuit for it?

By designing it, first.

  1. I realised Higher the Vcc value I take, the output increases more. Why?

Outputs often increase when they have access to increased voltage rail magnitudes.

  1. And what would be the ideal value?

In practice, it's a matter of compromise.

  1. Have I selected the wrong diodes? If I have so which one is suitable for the transistors I have chosen?

Lots of options. One is to use diode connected BJTs. Another is diodes. In either case, you may also want to add a resistor. You could also use a VBE multiplier, with or without Early Effect compensation. In most cases where more power is involved, you may want to thermally couple them. In this case, it perhaps matters not so much.

  1. Why is my positive output waveform increasing with each increasing second?

Not sure what you are noticing, even with the new diagram.

  1. Also why is my Ie of npn decreasing?

Not sure that curve is present, either.

From the datasheets on the BJTs you've selected, these are TO-92 packaging (which is anywhere from \$200\:\tfrac{^\circ \textrm{C}}{\textrm{W}}\$ to \$325\:\tfrac{^\circ \textrm{C}}{\textrm{W}}\$ -- and I'm not talking about SOT-23 here.) This basically means they can't dissipate much. Even with just \$100\:\textrm{mW}\$, you may see internal temperatures at anywhere from \$20\:^\circ \textrm{C}\$ to \$30\:^\circ \textrm{C}\$ rise over ambient. And that's only \$100\:\textrm{mW}\$.

You will need to reserve about \$1.2\:\textrm{V}\$ to keep both the NPN and the PNP in their active and not saturated regions. Assuming you were willing to run your BJTs at \$50\:^\circ \textrm{C}\$ over ambient (about a \$\tfrac{1}{5}\:\textrm{W}\$ each) you still probably wouldn't get any better than \$150\:\textrm{mW}\$ into an \$8\:\Omega\$ speaker when using the \$5\:\textrm{V}\$ rail that such an output power requires. That's how inefficient this design is likely to be.

Are you prepared for the paltry output that using these BJTs would normally imply?

(Also, as a side question that will rise up later on, how do you expect to handle the stereo output from your mobile? Will you select just one side or the other or do you require summing of the two channels into one?)

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